Steel foil



Feb. 21, 1967 E. J. SMITH ETAL STEEL FOIL original Filed Feb. a, 196s ATTORNEYS (saHaNl) saNxmHi United States Patent 3,305,323 STEEL FOIL Edwin J. Smith and Edward P. Spencer, Steubenville,

Ohio, assignors to National Steel Corporation, a corporation of Delaware Original application Feb. 8, 1963, Ser. No. 257,310, now Patent No. 3,214,820, dated Nov. 2, 1965. Divided and this application July 13, 1965, Ser. No. 482,967

11 Claims. (Cl. 29-180) This is a division of application Serial No. 257,310, filed February 8, 1963, now Patent No. 3,214,820.

The present invention is concerned with new flat rolled steel product and related strip steel finishing operations.

Production methods for flat rolled steel and the basic strip steel finishing processes and products have long been well established and standardized in the steel industry. Hot rolled products are reduced in hot strip mills to gages as thin as 0.0449 and then reduced in cold rolling mills to gages as thin as 0.006. In recent strip steel finishing operations, further cold reduction has produced thin tinplate gages as low as .004.

To a large extent, the physical properties of steel and its work-hardening characteristics are responsible for such standardization and have helped establish steels own boundaries in the fiat rolled metal field. For example, the Work-hardening properties of the above thin tinplate presented sufiicient problems to container makers, that further gage reductions, if contemplated, would merely have been rejected as presenting an uneconomical and unrealistic challenge.

Therefore, it has been natural for many engineering and consumer uses of thin gage flat rolled metal to be limited to high malleability, high ductility, low tensile strength, non-ferrous metals such as lead, tin, copper, and aluminum. The history of the metallic foil industry exemplies this. Composition foil (tin and lead) held practically the entire consumer market until another malleable metal, aluminum, became available in sufficient quantities. The metallic foil field also included other malleable metals such as copper and gold for special uses. To have attemptedto place finished steel strip in the metallic foil field would not only have been considered unrealistic but impossible to those skilled in the art.

There had been sound basis for such conclusions by` those skilled in the art. The great bulk of the strip steel finishing art is concerned with what is referred to as mild steel, i.e., a steel having up to .15% carbon. Mild steels work-hardening characteristics are well known and pref sent diflicult problems in the strip rolling and forming operations necessary today for both metal producer and fabricator. Under prior practice, to have suggested reducing mild steel beyond the thin tinplate stage, without a second anneal, would have been rejected as sure to produce an unusably hard product with a crystal structure which would cause edge cracking and bend breakage during processing. Therefore, cold reduction after the normal first cold rolling and annealing has been limited to 30% to 50% in the strip steel finishing art. The invention departs from these practices `of the prior art and includes teachings on products and processes of manufacture which realistically establish steel in the metallic foil art.

By way of example, tinplated steel foil :below a halfthousandth of an inch has been produced in accordance with the teachings of the invention without any of the problems developed in thin tin practice. It is springy and can be bent repeatedly through substantially 360 without cracking or breaking and can be crease folded and opened repeatedly without cracking or breaking. Coating adherence and coating protection are excellent.

after plating of substantially in excess of 50%,

and higher, without an anneal.

It has high tensile strength, from five to ten times that of aluminum foil of the same gage, is more abrasion-resistant than common foils, such as aluminum, yet can -be torn and cut readily. It has a smooth, fully plated, bright surface. Tests indicate that its corrosion resistance exceeds that which would be expected from the thickness of its tinplating which can be about two-millionths of an inch.

By virtue of the discovery that it was actually possible to make plated steel foil, the present invention dispelled the myth thatplated steel reduced more than the accepted range of 30% to 50% would be of no use in the as rolled condition because of work hardness and brittleness. The more common steel coating metals, such as tin, zinc, or aluminum, because of their low melting temperatures, precluded annealing plated strip steel. Reducing steel below the thin tin gage levels of forty to sixty poundsV per base box before plating would have required annealing and temper rolling before plating and these operations would have had to be performed on material which, especially in the case of annealing, could not be handled at the high strip speeds dictated by economic conditions in modern steel mills. Therefore, in effect, the difiiculties and problems the industry has encountered in fabricating the relatively hard thin tinplate for normal uses, such as canmaking, have acted to block an entire field of possible uses for any lighter gage steel, plated or otherwise. Part of the invention is the conception of numerous applications for a plated steel foil in modified and combined forms for packaging, for consumer and engineering uses, and for other industrial uses which have opened the door to many practical uses of steel foil in all forms.

In the metallic foil industry, as previously constituted, foil was dened as thin metal membrane of less than .006 thickness and was distinguished from metall of greater thickness called sheet, strip, or plate. Steel does not remain a pliable membrane up to .006 thickness. Steel of less than .006", say, .005, is not foil. Forexample, .005 tinplate and the lighter forty-pound per base box tinplate are available in the rigid can market for beer, oil, food, etc. Therefore, in describing the present invention, it becomes necessary to set limits for steel foil gages other than those laccepted for the common metals of the i foil industry. Steel foil, therefore, as referred to herein,

is defined as thin metal membrane of not greater than about .002 thickness. Further, steel foil, especially in a plated condition, is distinguished from lother fiat rolled finished steels, such as thin tinplate, 4by a cold reduction e.g. 70%

Of course, test standards for steel foil are not established. It has become obvious that testing apparatus and methods, e.g. Rockwell and Brinnell hardness, Pittsburgh lock-seam tests, and the like, customarily used in the steel industry, are not applicable to steel foil. At present, comparative tests withv other metal foils and steel products must be used. For example, steel foil has a tensile strength five to ten times greater than that of aluminum foil of the same gage. The abrasion resistance of steel, again partially dependent upon the plating, far exceeds that of aluminum, making tinplated steel foil,y for example', far superior to aluminum foil for many industrial uses.

It has been found that the springiness and other mechanical properties peculiar to steel in foil form can be Varied by the rolling procedure. For example, tinplate stock reduced in a single pass to foil gage is not as springy as tinplate stock reduced a total of 90% by cold rolling passes of from 20% to 30% reduction per pass. Both products have a similar appearance and both, in the as rolled condition, would be considered full hard but the springiness and other special mechanical properties peculiar to steel foil would differ.

Full hard, as known in the steel industry, may require further definition when applied to steel foils. Undoubtedly, both of the above 90% cold reduced samples have the strength and other properties associated with full hard as known in the steel industry but neither exhibits the ,poor bending qualities or brittleness ordinarily associated with full-hard steel which has been cold reduced 90%. Even when reduced to foil gages in a single pass of greater than 90% reduction, steel foil does not exhibit any of the brittleness expected. It can be bent and folded repeatedly without cracking. Some of the mechanical properties of foil are influenced considerably by the method and speed of reduction. It is believed that the heat produced during rolling has a greater effect, often instan-taneously, at the thin gages involved than would be the case with conventional steel strip.

Many desirable properties of plated steel foil materialize because of proper practice in the manufacture of plated steel foil. Again using tinplated steel foil by way of example only, it has been found very important in practice, for purposes of avoiding rolling and other problems, to metal coat the strip steel in an iron-alloy layer free manner. Ordinarily, this would involve either electroplating, gas plating, electrophoretic plating, and vapor plating, all herein embraced under the term 1p1-ating, however, some hot dip experts maintain that steel can be hot dip coated without an iron-alloy layer, and to the extent that this is possible, such a product could be used, especially with the heavier gage steel foils.

The present invention includes the discovery that a matte-finish tinplate is preferred as starting stock for tinplate foil. Practice with matte-finish tinplate substantiates the aforementioned teachings on avoidance of an alloy layer between the coating metal and the base metal. In ow brightening of electroplated tinplate, an alloy layer is formed. It has been found with .011" tinplate having one pound per base box of coating that the `ill effects of an alloy layer begin to show up at thicknesses of approximately two to three-thousandths of an inch. Tin-iron alloy crystals protrude through the coating and grey streaks show up on the surface of the product at about these thicknesses. Also, tin-iron alloy scale forms on the work rolls. The ymatte-finish of tin, zinc, and other coating metals is converted to a bright finish in rolling to the foil gages taught by the present invention.

In rolling plated strip steel to foil gages, work hardening properties of the coating metal can be critical. With finished strip steel currently available and that contemplated by the invention, reductions greater than 95% will take place without intermediate anneal. It has been found in cold reducing to foil gages that the coating metal reduces in proportion to the base metal. While the steel itself can be cold reduced in the prescribed ranges without an anneal, many of the coating metals included in the invention cannot withstand such cold reduction without an anneal. Therefore, it is necessary, in some instances, to match the cold reducing properties and thickness of the coating metal to the starting thickness of the steel base metal. For example, coating metal which will only reduce 60% without an anneal should be used only with a coated starting stock having a thickness gage calling for not more than 60% reduction to the nished foil. Otherwise, as the maximum permissible reduction without anneal is reached, coating metal will come off during contact with the work rolls. On the other hand, with many coating metals, this problem can be solved by the rolling practice. For example, controlling rolling lubricant temperature can add the necessary malleability to zinc and solve many work-hardening problems of low temperature anneal metals. Other metals such as tin are found to be self-annealing during cold rolling with or without control of lubricant temperature.

Where an annealing problem does exist with a coating metal, selected frequency induction heating can usually be readily matched to the needs of a particular problem because of the precisional control of temperature and heat penetration available. Induction and other forms of heating, such as hot oil baths, can also be used for heat treating the steel itself since the various effects of heat treatment such as stabilizing, strain relief, and softening occur readily and apparently at lower temperatures when dealing with foil gages.

The coating metal thickness, both starting and final, become more important when it is considered that plated steel foil will be reduced to gages as low as one tenthousandth of an inch (.0001). The combinations of plating thickness and steel base metal thickness gages available in foil form approach innity when it is considered that the foil can vary between about .002 and about .0001 and also that the initial coating weight can vary, with tin for example, from a flash coating up to several pounds per base box (217.78 sq. ft.). The scope of these variations can be best comprehended from a graphical representation such as that shown in the accompanying drawings, wherein:

FIGURE 1 is a graphical representation of the change in thickness of strip steel with percentage cold reductions falling within the scope of the present invention;

FIGURE 2 is a graphical representation of the change in thickness of certain tin coating weights applied to strip steel with percentage cold reductions falling within the scope of the present invention; and

FIGURE 3 is a graphical representation of the change in thickness of certain zinc coating weights applied t0 strip steel with percentage cold reductions falling Within the scope of the present invention.

Several examples from these graphical representations follow:

.010" blackplate reduced 90% will have a thickness of about .00l; if the blackplate had a coating of 1.5 lbs. of tin per base box, the coating thickness would be about nine-millionths of an inch @X10-6); if initial coating had been .25 lb. per base box, the coating thickness would have been one and six-tenths millionths of an inch (1.6)(10-6).

.005" blackplate, when reduced would have a thickness of .001; if the starting coating thickness was 1.5 lbs. of tin per base box, the final thickness woulde be about seventeen and one-half millionths inch (17.5)(10-6); if the coating weight initially applied was .5 lb. per base box, the final thickness would be about six-millionths inch (6X10-6).

The infiinte number of variations available can be conceived by combining the graphical representations of FIGURES 1 and 2 for tin or FIGURES l and 3 for zinc. Other coating metal combinations, dependent on practical initial coating thickness limits, can be obtained in like manner. In this regard, while examples from experience with tin, zinc, zinc alloy, aluminum, aluminum alloy, stainless type steel, and titanium, will predominate in this disclosure, the invention is not so limited. Conventional strip steel finishing operations are concerned with various protective coatings for steel; similarly, with the present invention. Among the metallic coatings to be considered are the following metals and their alloys-tin, terne, zinc, aluminum, copper, nickel, chromium, cadmium, stainless steel, silver, gold, and titanium. Special consideration will be given to a steel foil plated with stainless type steel. As a practical matter, strip steel can be coated economically with most of the aforementioned metals, without an alloy layer, with coatings up to .001" thick and higher in continuous strip lines. For example, referring to FIGURE 3, .6 ounce per square foot of zinc has a thickness of .001.

As defined, plated steel foil includes gages up to about two one-thousandths of an inch (.002) made by a cold reduction of cold reduced and annealed strip stock substantially in excess of 50%, with cold reductions of 97% and higher being contemplated. Therefore, starting material for the present invention can be conventional steelv mill product. Plated strip steel having a thickness of about sixty-live thousandths inch (.065"), when reduced approximately 97%, will have a gage of about two thousandths of an inch (.002).v It is realized that the lowest starting gage, illustrated in FIGURE 1 (.003"), is below the tinplate gage conventionally rolled as thin tinplate today; however, such thickness is believed to be possible by thin tinplate processes. For purposes of the present invention, thin tinplate includes products variously referred to as double reduced tinplate, thin tin, and ductile thin tin. Thin tinplate is made by applying a second cold reduction of between 30% and 50% to conventional cold rolled and annealed blackplate before plating.

Cold reduction can be carried out by cold rolling passes of as low as reduction per pass or up to 90% or higher reduction per pass. Certain plated stock, such as tinplate, can take large cold reductions readily Without any visible effect on the coating or the strip; it is believed that the lubricity of tin aids in this respect. Simil-ar experience has been had with zinc, aluminum, aluminum alloy, stainless type coatings and titanium. At thin gages, tinplated steel foil yand steel plated with any of the malleable metals included in this invention may be reduced two strands at a time by rolling the strands back to back through the cold reducing mill.

The amount of cold reduction per pass is largely determined by the economics of the process and, tosome extent, by the desired properties of thel finished product and the cold reducing properties of the coating. The following table will help illustrate why economics enters into this determination. This table shows the number *of passes required at various percentages to reduce material having starting gages of .005", .0072, and .0011 to a foil of .0005.

TABLE I.NUMBER OF COLD ROLLING PASSES RE- QUIRED TO PRODUCE .0005I FOIL Percent; Starting Gage Reduction per Pass It will be observed from FIGURE 1 that the total reduction required to produce most of the f 'l gages from the standard gages of strip steel would requiie a reduction of substantially 70% or higher. If such cold reductions are carried out with less than 40% reduction per pass, the number of passes required is high for ordinary steel mill practice. Therefore, the aim is to have the reduction per pass exceed 40%; but, consideration must be given to the desired properties of the foil and-the effect of large cold reductions on the coating. Reductions in the range of 40% to 60% per pass are preferable. Larger cold reductions per pass tend to reduce the springiness of the foil and special consideration must be given to the foil which should be either self-annealing or permit a cold reduction in the range desired without an anneal and should exhibit high malleability. The large cold reductions and fine gages required to produce steel foil can be handled well with a cold rolling mil-l of the Senzimir type. The properties and the pressure and tension controls available on this type of mill are well known in the art so that no further description of a Senzimir mill is necessary to an understanding of the invention.

By making economically feasible reduction of plated steel strip to foil gages, the invention makes possible many new consumer and engineering use products. Also, many existing products can be fabricated more economically. Many of the new uses and new products of plated steel in foil gages result from the combination of high tensile strength steel with the special properties of a coating metal such as copper, cadmium, silver, and the like. Copper plated steel strip, for example, reduced to foil gages, can

be used to form rea-ctance devices, coil windings, ca-

pacitors, etc., can be used in plural layers to make pliable short radius turn conductors, and can be used in other similar uses which take advantage of the high electrical conductivity of the surface layer copper and the high tensile strength and excellent handling properties of the steel. Silver-plated steel foil can qualify ecomoni-cally for many special electrical uses from which it had previously been barred and, similarly, for cadmium and cadmium alloy plated steel foil.

While aluminum plated steel foil also has many electrical applications because of its good electrical conductivity, it and some of its alloys such as aluminum-manganese will be considered with tin and zinc for making many products where corrosion protection is the most important function of the coating metal. Steel foil, plated with any of these coating metals, has numerous uses in packaging,

building, decorating, making special textiles, and numerous other industrial applications. These uses are multiplied by the advantages of laminating steel foil which will be considered later.

In packaging, for example, metal plated steel foil from about .0001 to about .0007" has many of the normal consumer foil uses especially in industrial wrapping. Metal plated steel foil up to about .001 or .0015" makes excellent foil pouches for freeze-dry products, and the like, where creating a light and vapor barrier is important. While plated steel foil of various gages up to about .002 makes excellent semi-rigid packaging tray structures such as that used for precooked frozen foods, etc., the advantages of all these packaging and other uses over other metallic foils is the high tensile strength of the steel, its abrasion resistance, and the easy handling properties which permit fabricating with much less ditiiculty than the other metallic foils. These properites are especially helpful in handling the ne foil gages used for label stock.

In the building industry, any of the lower cost coating met-al foils can be used for Water vapor barrier and insulation purposes more economically than metallic foils currently available. Special corrosion protection and strength characteristics for many products are available with titanium plated steel foil. Honeycomb core and expanded metal are typical applications for such foil, as Well as for foils plated with the more common corrosion-resistant metals such 'as tin, zinc, and aluminum.

Nickel and some of the nickel alloy plated steel foils find special uses, along with copper and copper alloy plated steel foils, in the decoration and novelty fields. These and some of the lower-priced metal plated steel foils of the lower thickness gages can also be readily slit into ne thread providing metallic textile materials of higher strength than any currently available.

In making products from steel foil, the lfabrication may employ folding, die forming, scoring, embossing, and/or a variety of forms of printing. Other uses than those specically enumerated `above will be obvious from the present disclosure and are considered to be within the scope of the present invention.

Stainless steel plated steel foil can be produced by several methods in accordance with the teachings of the invention. In this context, stainless steel is used in its broad sense, including what is often referred to in the .art as a stainless type steel or merely stainless As such, utilization of nickel and/or chromium, or alloys thereof, as an alloying agent(s) in sufficient quantities to make steel rust and corrosion resistant are included, One

method is plating mild steel with stainless steel and reducing as previously described. Other methods involve plating mild steel strip with chromium and/or nickel, or their alloys. Heat diffusion applied to the plated strip or after the plated strip has been reduced to foil gages produces stain-less steel plated foil. Methods and apparatus for causing heat diffusion of plated metals are known in the art so tha-t no further description is necessary to an understanding of this phase of the invention. However, cold reduction practice within the scope of the present invention has been found to produce stainless plated steel foil without heat diffusion; for example, mild steel simultaneously plated with chromium and nickel and then cold reduced to foil gages produces highly satisfactory stainless plated steel foil. The savings involved in such a process are obvious. Various new industrial, commercial and consumer uses of stainless plated steel foil building structures, such as honeycomb panels, in the packaging industry for disposable containers, wrappings, laminated and otherwise, have been developed as a result yof this new product.

The invention also includes the lamination of steel foil, plated or unpflated, wi-th one ormore of the following materials: paper, paperboard, Mylar and other film materials, heat sealing lms, natural and synthetic textiles, felts, fibers, and filaments, plastic, fiber, and wood sheeting, or other metals. The steel foil and lamina are normally joined `by an adhesive which may be heat or pressure sealed in continuous-line operations. Steel foil has special advantages over other metallic foils for laminated products and in manufacture of laminated products because of the high tensile strength and abrasion resistance of steel foil. Through this invention, all the advantages of steel or all the advantages of steel and a plating metal can be added to the properties of other laminating materials making various new products economically feasible. The uses of laminated steel foil extend to all the uses in industries referred to earlier in relation to non-laminated steel and are expanded lby properties and uses for the laminating material itself.

Many of the laminae set forth above may be joined by pressure or heat to the steel foil, may be spray coated, or may be joined by use of adhesives. In formulating an adhesive, the material to be laminated to the steel f-oil and the surface character of .the foil should be considered. Most suitable adhesives can be formulated from basic latex and resin base adhesives including epoxy resin compounds, vinyl phenolics, and rubber-base adhesive such as neoprene. The proper formulation can take care of foil surface oil problems but, in the interest of uniform adherence, the foil surface may be cleaned by cathode cleaning, vapor cleaning, or solvent wipe or rinse. Often merely heating the foil will evaporate the oil and provide uniformity. For example, tinplated foil heated to about 300 F. .provided uniform lamination using the adhesive referred to in the trade as Polybond.

In disclosing the invention, specific descriptions of several products and processes were resorted to in the interest of clarity; the scope of the invention is not to ybe limited by such description but is to be determined by the appended claims.

What is claimed is:

1. Cold reduced, flat rolled, full-hard non-embrittled steel foil coated with metal, selected from the group consisting of tin, terne, zinc, aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, chromium, chromium alloy, cadmium, stainless steel, stainless type steel,

silver, gold, and titanium and having a total thickness gage ybetween about .0001 `and .002.

2. Flat rolled steel foil having a thickness Igage between about .0001" and .002" characterized by f-ull hardness produced by cold rolling reduction in excess of without anne-al and Ifurther characterized by absence of brittleness and absence of poor 'bending qualities normally associated with mild steel cold reduced in excess of 70% without an anneal.

3. Metal packaging stock comprising metal plated, cold reduced, at rolled, 4full-hard, non-embrittled steel foil having a thickness gage between about .0001 and about .001".

4. A new article of manufacture comprising metal plated, cold reduced, fiat rolled, full-hard, non-embrittled steel foil having a thickness gage between about .0001 and .002 and coated on at least one surface with a nonmetallic lamina.

v5. A new article of manufacture comprising cold reduced, flat rolled, full-hard, non-embrittled steel foil having a thickness gage between about .0001I and .002" and coated on at least one surface with a non-metallic lamina.

6. A semi-rigid packaging tray structure formed from metal plated, cold reduced, lflat rolled, full-hard, non-embrittled steel( foil having a thickness gage 'between about .0005 and .002".

7. A semi-rigid packaging tray structure formed from cold reduced, at rolled, full-hard, non-embrittled steel -foil having a thickness gageI between about .0001 and .002 and coated with a non-metallic lamina.

8. Packaging material comprising cold reduced, flat rolled, yfull-hard, non-em'brittled steel foil having a thickness 4gage between about .0001 and .002" and at least partially coated with a heat-sensitive sealing material.

9. Laminated rigid structure comprising cold reduced, fiat rolled, full-hard, non-embrittled steel foil bonded to a non-metallic backing material, ythe steel foil having a thickness gage fbetween about .0001 and .002.

10. An electrical conductor comprising metal plated, cold reduced, tiat rolled, full-hard, non-embrittled steel foil lhaving a thickness gage lbetween about .0001" and .002", the metal plating being selected from the group consisting of aluminum, cadmium, silver, tin and copper.

11. An electrical reactance device comprising electrically insulated convolutions of metal plated, cold reduced, at rolled, full-hard, non-embrittled steel foil having a metal plating selected from the group consisting of aluminum, silver and copper with the steel yfoil and metal plating having a total thickness gage between .0001 and about .001.

References Cited b y the Examiner UNITED STATES PATENTS 1,340,149 5/1920 Browne 29-183.5 1,709,801 4/1929 Muller 29-183.5 X 1,979,539 11/1934 Gardner et al. 29-183.5 X 1,982,587 11/1934 Wilkins 29-183.5 2,116,107 5/1938 Erb 29--196.4

DAVID L. RECK, Primary Examiner.

lR. O. DEAN, Assistant Examiner. 

2. FLAT ROLLED STEEL FOIL HAVING A THICKNESS GAGE BETWEEN ABOUT .0001" AND .002" CHARACTERIZED BY FULL HARDNESS PRODUCED BY COLD ROLLING REDUCTION IN EXCESS OF 70% WITHOUT ANNEAL AND FURTHER CHARACTERIZED BY ABSENCE OF BRITTLENESS AND ABSENCE OF POOR BENDING QUALITIES NORMALLY ASSOCIATED WITH MILD STEEL COLD REDUCED IN EXCESS OF 70% WITHOUT AN ANNEAL. 